1. Field of the Invention
This invention relates in general to an electron beam measuring instrument which includes a first electron beam source which is directed on a first beam axis and a second electron beam source arranged on a second beam axis and includes a focusing deflection unit for stigmatic imaging of the second electron beam source in an intermediate image which is on the first beam axis.
2. Description of the Related Art
The publication Microelectronic Engineering, Vol. 7 (1987) pages 163 through 172 discloses an electron beam measuring instrument which is optimized for low accelerating voltages in the range of 0.5-2.5 kV with which the voltage distribution in components of microelectronics can be read with a spatial resolution of about 0.1 .mu.m and the voltage waveform at interconnects up to 0.5 .mu.m wide can be stroboscopically registered with a temporal resolution of about 100 through 200 ps using the conventional beam blanking system.
The publication Applied Physics Letters 51 (2) 1987, pages 145 through 147 discloses a scanning electron microscope which has a thermal LaB.sub.6 or a field emitter gun which are replaced by a photo-cathode charged with a pulsed laser beam with a pulse repetition rate of 100 MHz and a pulse width of 1 through 2 ps. Since the width of the photo-electron pulses which are generated roughly corresponds to the width of the laser pulses which trigger the photo emission, this system is particularly suited for stroboscopic measurements in fast gallium-arsenide circuits having a temporal resolution which lies in the picosecond range. The spatial resolution roughly corresponds to that of the scanning electron microscope which has a conventional beam generator.
The publication Microelectronic Engineering, Vol. 4, No. 2 1986 pages 77 through 106 discloses methods for imaging the voltage distribution in VLSI circuits which require a continuous electron beam or, respectively, a pulsed electron beam which has a comparatively low particularly a variable pulse repetition rate (fp.apprxeq.1-10 MHz). These methods which are indispensable for fast testing of the functioning of the microelectronic components can only be poorly implemented with the known electron beam measuring instrument due to the pulse repetition rate which is rigidly prescribed by the laser system.